I’ve never owned or lived in one, so I can’t comment on costs for heating and cooling. However, my aunt and uncle lived in one in Colorado and it was very cool. I remember it being very spacious. The main level was pretty open. You walked in and saw the living area, dining area, and kitchen, then past the kitchen was a closed wall with a door (divided space) and there was a bathroom and possibly a bedroom. The ceiling was high in the bottom living space, then a bit less than half the dome had been made into an upper level for bedrooms. You went up a set of stairs and it was like a long, open hallway with a railing, the bedrooms accessible from the hall. The rooms were closed by walls and doors (divided space). My aunt and uncle were able to use a good deal of the space and the house felt light and airy. I don’t know enough about thermodynamics to speculate on how well the house kept cool/warm or whether the dome design helped in this regard.